At least six policemen and a civilian have been killed by a roadside bomb in eastern Sri Lanka, the authorities say.

Another 12 officers who were on the bus taking them on leave were hurt in the explosion, which happened close to a university in Batticaloa district. The Defence Ministry blamed Tamil Tiger rebels for the blast. Violence has risen in Sri Lanka in recent months as the country has slid back towards war, despite a 2002 ceasefire still in place. The police officers? bus was heading out of Batticaloa when the attack took place, according to a spokesman for Sri Lanka?s security forces. Brigadier Prasad Samarasinghe said a claymore mine, which fires shrapnel horizontally, was detonated by the roadside.

A statement from the Defence Ministry blamed Tamil Tiger ?terrorists? for the attack. The east of Sri Lanka has seen much fighting in recent months. The military has driven the rebels from towns and villages along the coast they had controlled for more than a decade and tens of thousands of civilians have moved into refugee camps.

The Tamil Tigers have withdrawn to jungle areas where Sri Lankan soldiers and commandoes are continuing operations against them. Reporters in Colombo says the rebels have vowed to hit back, and now describe themselves as being in guerrilla mode in the east after losing territory.